Pneumatic Tire

ABSTRACT

A pneumatic tire comprises a tread portion; a plurality of main grooves extending in a tire circumferential direction in a tread surface of the tread portion, at least one of the plurality of main grooves having a wave-like shape with periodic oscillation; a plurality of land portions adjacent to one another in a tire lateral direction formed by the plurality of main grooves; and a plurality of projections disposed on a groove bottom of the wave-shaped main groove disposed in a row in the tire circumferential direction in accord with periodic oscillations of the wave-shaped main groove.

TECHNICAL FIELD

The present technology relates to a pneumatic tire that can provideimproved braking performance on wet road surfaces.

BACKGROUND ART

The conventional pneumatic tire described in Japanese Unexamined PatentApplication Publication No. 2014-076764, for example, is designed toimprove both wet performance (braking performance on wet road surfaces)and noise performance (anti-external noise performance). This pneumatictire includes a plurality of wave-shaped circumferential groovesextending in the tire circumferential direction with left and rightgroove walls having a wave-like shape with a wavelength and anamplitude, and at least one row of wave-shaped land portions defined byadjacent wave-shaped circumferential grooves. The shape of the left andright groove walls of the wave-shaped circumferential grooves haveidentical wavelengths but with a phase difference. The groove wall onthe wave-shaped land portion side of one of the left and rightwave-shaped circumferential grooves that define the row of wave-shapedland portions has an amplitude that is greater than that of the groovewall on the wave-shaped land portion side of the other wave-shapedcircumferential groove.

The conventional heavy duty pneumatic tire described in JapaneseUnexamined Patent Application Publication No. 61-175104, for example, isdesigned to improve both wet performance (braking performance on wetroad surfaces) and uneven wear resistance performance. This heavy dutypneumatic tire includes a tread that includes at least three maingrooves extending in the tire circumferential direction in a zigzagmanner that define the tread in the tire lateral direction, shoulderribs located at least on the outermost sides in the tire lateraldirection on the tread, and second ribs inwardly adjacent to theshoulder ribs that divide the main grooves. The ridge lines of theshoulder ribs and the second ribs that face the main grooves locatedoutward in the tire lateral direction have a smaller zigzag pitch andamplitude.

The conventional pneumatic tire described in Japanese Unexamined PatentApplication Publication No. 2014-094645 is designed to provide reducedair column resonance formed in the circumferential main groovesextending in the circumferential direction while maintaining orenhancing hydroplaning resistance performance. This pneumatic tireincludes circumferential main grooves and lug grooves that extend fromthe circumferential main grooves outward in the tire lateral direction;wherein near an intersection portion where the circumferential maingrooves and the lug grooves meet, at least two projections that projectfrom the groove bottom are provided spaced apart from each other, and apath is formed between adjacent projections. The path includes an inletopening on the side distal from the lug groove and an outlet opening onthe side proximal to the lug groove, the cross-sectional area of theinlet opening being greater than that of the outlet opening.

In the pneumatic tire of Japanese Unexamined Patent ApplicationPublication No. 2014-076764 described above, the wave-like shape of theleft and right groove walls of the wave-shaped circumferential groovesprovide improved braking performance on wet road surfaces. However,improvements in vehicle performance have led to demands for furtherenhancements in braking performance on wet road surfaces. In the heavyduty pneumatic tire of Japanese Unexamined Patent ApplicationPublication No. 61-175104 described above, the ridge lines of theshoulder ribs and the second ribs that face the main grooves locatedoutward in the tire lateral direction have a smaller zigzag pitch andamplitude. The resulting difference in rigidity may adversely affectwear resistance performance. Additionally, the corner portions formed bythe zigzag shape of the main grooves may experience uneven wear.Additionally, in the pneumatic tire of Japanese Unexamined PatentApplication Publication No. 2014-094645 described above, water flowsfrom the main groove to the lug groove through the path between theprojections disposed on the groove bottom. However, improvement indrainage properties is stopped at one portion of the main grooves wherethe lug groove is disposed.

SUMMARY

The present technology provides a pneumatic tire that can provideimproved braking performance on wet road surfaces.

A pneumatic tire according to an embodiment of the present technologycomprises:

a tread portion;

a plurality of main grooves extending in a tire circumferentialdirection in a tread surface of the tread portion, at least one of theplurality of main grooves having a wave-like shape with periodicoscillation;

a plurality of land portions adjacent to one another in a tire lateraldirection formed by the plurality of main grooves; and

a plurality of projections disposed on a groove bottom of thewave-shaped main groove disposed in a row in the tire circumferentialdirection in accord with periodic oscillations of the wave-shaped maingroove.

According to the pneumatic tire, the main grooves have a wave-like shapewith periodic oscillation. This increases the overall width of the maingrooves to provide good drainage properties, and allows brakingperformance on wet road surfaces to be improved. Furthermore, accordingto the pneumatic tire, the projections provided on the groove bottom ofthe wave-like main grooves makes the water at the groove bottom of themain groove turbulent to spread out and discharge the water out of themain groove. This allows good drainage properties to be provided andbraking performance on wet road surfaces to be improved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein, the plurality of projections aredisposed in a plurality of rows in the tire lateral direction.

According to the pneumatic tire, the projections are disposed in rows inthe tire lateral direction. This allows the water located outward of themain groove in the tire lateral direction to be spread out anddischarged. Thus, drainage properties can be further improved andbraking performance on wet road surfaces can be improved.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein, the plurality of projections have aprojection height from the groove bottom less than that of a wearindicator disposed on the groove bottom of the wave-shaped main groove.

According to the pneumatic tire, the projections are formed with a lowerprojection height from the groove bottom than a wear indicator, which isa projection within the main groove that allows the degree of wear to bevisually determined. This prevents the function of the wear indicatorfrom being inhibited by the projections.

A pneumatic tire according to an embodiment of the present technologymay have a configuration wherein,

four of the plurality of main grooves are provided in the tread surface,each having periodic oscillation;

a center land portion, middle land portions adjacent to the center landportion on either side in the tire lateral direction, and shoulder landportions outwardly adjacent to the middle land portions in the tirelateral direction are formed by the plurality of main grooves; and

the main grooves between the center land portion and the middle landportions comprise the projections.

According to the pneumatic tire, the projections are disposed to providegood drainage properties in the main grooves between the middle landportions on either side of the center land portion, which is the centerland portion in the center of the tread surface that contributes to thebraking performance on wet road surfaces. This allows the obtainedeffect of improving braking performance on wet road surfaces to besignificant.

A pneumatic tire according to an embodiment of the present technologycan provide improved braking performance on wet road surfaces.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 2 is a plan view of a tread portion of a pneumatic tire accordingto an embodiment of the present technology.

FIG. 3 is an enlarged cross-sectional view of a main groove of apneumatic tire according to an embodiment of the present technology.

FIG. 4 is an enlarged cross-sectional view of a lug groove of apneumatic tire according to an embodiment of the present technology.

FIG. 5 is an enlarged cross-sectional view of a narrow groove of apneumatic tire according to an embodiment of the present technology.

FIG. 6 is an enlarged cross-sectional view of a lug narrow groove of apneumatic tire according to an embodiment of the present technology.

FIG. 7 is an enlarged cross-sectional view of a main groove of apneumatic tire according to an embodiment of the present technology.

FIG. 8 is a plan view of a tread portion of a pneumatic tire of anotherexample according to an embodiment of the present technology.

FIG. 9 is a table showing the results of performance tests of pneumatictires according to Examples of the present technology.

DETAILED DESCRIPTION

Embodiments of the present technology are described in detail belowbased on the drawings. However, the present technology is not limited tothese embodiments. Constituents of the embodiments include elements thatcan be easily replaced by those skilled in the art and elementssubstantially the same as the constituents of the embodiments.Furthermore, the modified examples described in the embodiments can becombined as desired within the scope apparent to those skilled in theart.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire accordingto the present embodiment. FIG. 2 is a plan view of a tread portion ofthe pneumatic tire according to the present embodiment. FIG. 3 is anenlarged cross-sectional view of a main groove of the pneumatic tireaccording to the present embodiment. FIG. 4 is an enlargedcross-sectional view of a lug groove of the pneumatic tire according tothe present embodiment. FIG. 5 is an enlarged cross-sectional view of anarrow groove of the pneumatic tire according to the present embodiment.FIG. 6 is an enlarged cross-sectional view of a lug narrow groove of thepneumatic tire according to the present embodiment.

Herein, “tire radial direction” refers to the direction orthogonal tothe rotation axis (not illustrated) of a pneumatic tire 1. “Inward inthe tire radial direction” refers to the direction toward the rotationaxis in the tire radial direction. “Outward in the tire radialdirection” refers to the direction away from the rotation axis in thetire radial direction. “Tire circumferential direction” refers to thecircumferential direction with the rotation axis as the center axis.“Tire lateral direction” refers to the direction parallel with therotation axis. “Inward in the tire lateral direction” refers to thedirection toward a tire equatorial plane (tire equator line) CL in thetire lateral direction. “Outward in the tire lateral direction” refersto the direction away from the tire equatorial plane CL in the tirelateral direction. “Tire equatorial plane CL” refers to the planeorthogonal to the rotation axis of the pneumatic tire 1 that passesthrough the center of the tire width of the pneumatic tire 1. “Tirewidth” is the width in the tire lateral direction between componentslocated outward in the tire lateral direction, or in other words, thedistance between the components that are the most distant from the tireequatorial plane CL in the tire lateral direction. “Tire equator line”refers to the line along the tire circumferential direction of thepneumatic tire 1 that lies on the tire equatorial plane CL. In thepresent embodiment, the tire equator line and the tire equatorial planeare both denoted by reference sign CL.

As illustrated in FIG. 1, the pneumatic tire 1 is mainly used onpassenger vehicles and includes a tread portion 2, shoulder portions 3on opposite sides of the tread portion 2, and sidewall portions 4 andbead portions 5 continuing in that order from the shoulder portions 3.The pneumatic tire 1 also includes a carcass layer 6, a belt layer 7,and a belt reinforcing layer 8.

The tread portion 2 is made of rubber material (tread rubber), isexposed on the outermost side of the pneumatic tire 1 in the tire radialdirection, and the surface thereof constitutes the contour of thepneumatic tire 1. The outer circumferential surface of the tread portion2 is a tread surface 21 that mainly comes into contact with a roadsurface when the tire runs.

The shoulder portions 3 are portions located outward in the tire lateraldirection on both sides of the tread portion 2. Additionally, thesidewall portions 4 are exposed on the outermost sides of the pneumatictire 1 in the tire lateral direction. The bead portions 5 each include abead core 51 and a bead filler 52. The bead core 51 is formed by a beadwire, which is a steel wire, wound into an annular shape. The beadfiller 52 is a rubber material that is disposed in the space formed byan end of the carcass layer 6 in the tire lateral direction folded backat the position of the bead core 51.

The end portions of the carcass layer 6 in the tire lateral directionare folded back around the pair of bead cores 51 from inward to outwardin the tire lateral direction, and the carcass layer 6 is stretched in atoroidal shape in the tire circumferential direction to form theframework of the tire. The carcass layer 6 is constituted by a pluralityof coating-rubber-covered carcass cords (not illustrated) disposed inalignment at an angle with respect to the tire circumferential directionthat conforms with the tire meridian direction. The carcass cords aremade of organic fibers (for example, polyester, rayon, and nylon). Atleast one carcass layer 6 is provided.

The belt layer 7 has a multilayer structure in which at least two belts71, 72 are layered. In the tread portion 2, the belt layer 7 is disposedoutward of the carcass layer 6 in the tire radial direction, i.e. on theouter circumference thereof, and covers the carcass layer 6 in the tirecircumferential direction. The belts 71 and 72 each include a pluralityof coating-rubber-covered cords (not illustrated) disposed in alignmentat a predetermined angle with respect to the tire circumferentialdirection (for example, from 20° to 30°). The cords are made of steel ororganic fibers (for example, polyester, rayon, and nylon). Moreover, thebelts 71 and 72 overlap each other and are disposed so that thedirection of the cords of the respective belts intersect each other.

The belt reinforcing layer 8 is disposed outward of the belt layer 7 inthe tire radial direction, i.e. on the outer circumference thereof, andcovers the belt layer 7 in the tire circumferential direction. The beltreinforcing layer 8 includes a plurality of coating-rubber-covered cords(not illustrated) disposed in alignment in the tire lateral directionsubstantially parallel (±5°) with the tire circumferential direction.The cords are made of steel or organic fibers (for example, polyester,rayon, and nylon). The belt reinforcing layer 8 illustrated in FIG. 1 isdisposed so as to cover end portions in the tire lateral direction ofthe belt layer 7. The configuration of the belt reinforcing layer 8 isnot limited to that described above. Although not illustrated in thedrawings, a configuration may be used in which the belt reinforcinglayer 8 is disposed so as to cover the entire belt layer 7.Alternatively, for example, a configuration with two reinforcing layersmay be used, in which the inner reinforcing layer in the tire radialdirection is formed larger than the belt layer 7 in the tire lateraldirection so as to cover the entire belt layer 7, and the outerreinforcing layer in the tire radial direction is disposed so as to onlycover the end portions of the belt layer 7 in the tire lateraldirection. In another example, a configuration with two reinforcinglayers may be used, in which both of the reinforcing layers are disposedso as to only cover the end portions of the belt layer 7 in the tirelateral direction. In other words, the belt reinforcing layer 8 overlapswith at least the end portions of the belt layer 7 in the tire lateraldirection. Additionally, the belt reinforcing layer 8 is constituted ofa band-like strip material (having, for example, a width of 10 mm) woundin the tire circumferential direction.

For the pneumatic tire 1 according to the present embodiment, thevehicle inner/outer side orientation when the pneumatic tire 1 ismounted to a vehicle is designated. In other words, when the pneumatictire 1 is mounted on a vehicle, the orientation with respect to theinner side and the outer side of the vehicle in the tire lateraldirection is designated. While the designated orientation is notillustrated in the drawings, the orientation is indicated, for example,by an indicator provided on the sidewall portion 4. For the pneumatictire 1, the side facing the inner side of the vehicle when mounted onthe vehicle is referred to as a “vehicle inner side” and a side facingthe outer side of the vehicle is referred to as a “vehicle outer side”.Note that the designations of the vehicle inner side and the vehicleouter side are not limited to cases where the tire 1 is mounted on avehicle. For example, rims have an orientation with respect to the innerside and outer side of the vehicle in the tire lateral direction. Thus,when the pneumatic tire 1 is mounted on a rim, the orientation withrespect to the vehicle inner side and the vehicle outer side in the tirelateral direction is designated.

As illustrated in FIGS. 1 and 2, in the pneumatic tire 1 as describedabove, four main grooves 22 extending in the tire circumferentialdirection are formed in the tread surface 21 of the tread portion 2.

The main grooves 22 include two center main grooves 22A disposedadjacent to the center in the tire lateral direction on either side ofthe tire equatorial plane CL and shoulder main grooves 22B disposedoutward of the center main grooves 22A in the tire lateral direction.Additionally, five land portions 23 are formed by the main grooves 22 inthe tread surface 21. The land portions 23 include a center land portion23A disposed between the center main grooves 22A and on the tireequatorial plane CL; middle land portions 23B disposed between thecenter main grooves 22A and the shoulder main grooves 22B and outwardlyadjacent to the center land portion 23A in the tire lateral direction;and shoulder land portions 23C disposed outward of the shoulder maingrooves 22B in the tire lateral direction, outwardly adjacent to themiddle land portions 23B in the tire lateral direction, and outermost inthe tread portion 2 in the tire lateral direction.

The main grooves 22 (22A, 22B) have a wave-like shape with periodicoscillation and a constant groove width W1 in the tire circumferentialdirection. The wave-like shape of the main grooves 22 can be such that agroove bottom 22 a illustrated in FIG. 3 has a linear shape in the tirecircumferential direction and groove walls 22 b have periodicoscillation such that the groove width W1 is constant in the tirecircumferential direction. Alternatively, the wave-like shape of themain grooves 22 can be such that the groove bottom 22 a and the groovewalls 22 b illustrated in FIG. 3 have periodic oscillation such that thegroove width W1 is constant in the tire circumferential direction. Inthe present embodiment, as illustrated in FIG. 3, the main grooves 22are formed with a chamfer 22 c on the opening edges. The groove width W1of the main grooves 22 is the opening width to the tread surface 21.Thus, the groove width W1 of the main grooves 22 with the chamfer 22 cis the groove width W1 between the outer edges of the chamfers 22 c. Asillustrated in FIG. 3, the center main grooves 22A of the main grooves22 has a groove width W1 ranging from 5 mm to 12 mm and a groove depthD1 ranging from 4 mm to 8 mm. The shoulder main grooves 22B have agroove width W1 ranging from 3 mm to 6 mm and a groove depth D1 rangingfrom 4 mm to 8 mm. The groove width W1 of the center main grooves 22A isgreater than that of the shoulder main grooves 22B. For example, thegroove width W1 of the shoulder main grooves 22B ranges from 10% to 50%of the groove width W1 of the center main grooves 22A. This ispreferable to maintain the drainage properties of the center maingrooves 22A and to ensure the rigidity of the land portions 23 aroundthe shoulder main grooves 22B. Additionally, as illustrated in FIG. 2,the center main grooves 22A of the main grooves 22 have a central line22 d of oscillation located a distance L1 outward from the tireequatorial plane CL in the tire lateral direction, the distance L1 beinga distance ranging from 20% to 30% of a ground contact width TW. Theshoulder main grooves 22B have a central line 22 d of oscillationlocated a distance L2 outward from the tire equatorial plane CL in thetire lateral direction, the distance L2 being a distance ranging from60% to 70% of the ground contact width TW. This is preferable tomaintain the drainage properties of the center main grooves 22A and toensure the rigidity of the land portions 23 around the shoulder maingrooves 22B. The edge shape and dimensions of the land portions 23 inthe tire lateral direction can be determined depending on theoscillation and position in the tire lateral direction of the maingrooves 22.

Herein, “ground contact width TW” refers to the width of the groundcontact region in the tire lateral direction. Additionally, theoutermost edges of the ground contact region in the tire lateraldirection are referred to as ground contact edges T. FIG. 2 illustratesthe ground contact edges T as being continuous in the tirecircumferential direction. The ground contact region is the region wherethe tread surface 21 of the tread portion 2 of the pneumatic tire 1comes into contact with a dry, flat road surface, when the pneumatictire 1 is mounted on a regular rim, inflated to the regular internalpressure, and loaded with 70% of the regular load. “Regular rim” refersto a “standard rim” defined by the Japan Automobile Tyre ManufacturersAssociation Inc. (JATMA), a “design rim” defined by the Tire and RimAssociation, Inc. (TRA), or a “measuring rim” defined by the EuropeanTyre and Rim Technical Organisation (ETRTO). “Regular internal pressure”refers to “maximum air pressure” defined by JATMA, a maximum value givenin “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, or “INFLATION PRESSURES” defined by ETRTO. “Regular load” refers a“maximum load capacity” defined by JATMA, the maximum value given in“TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA,and a “LOAD CAPACITY” defined by ETRTO.

In the pneumatic tire 1 according to the present embodiment, the middleland portion 23B on the vehicle inner side is provided with an auxiliarygroove 24 extending in a linear manner in the tire circumferentialdirection. The auxiliary groove 24 has a smaller groove width than themain groove 22 with the smallest groove width W1. The auxiliary groove24 is centrally disposed between the center main groove 22A and theshoulder main groove 22B that form the middle land portion 23B on thevehicle inner side. The auxiliary groove 24 divides the middle landportion 23B on the vehicle inner side into rib land portions adjacent inthe tire lateral direction. The auxiliary groove 24 has a groove widthranging from 1 mm to less than 3 mm and a groove depth ranging from 4 mmto 8 mm.

In the pneumatic tire 1 according to the present embodiment, the landportions 23 are provided with lug grooves 25 and narrow grooves 26 thatintersect the tire circumferential direction. The lug grooves 25provided in the center land portion 23A are referred to as center landportion lug grooves 25A, the lug grooves 25 provided in the middle landportions 23B are referred to as middle land portion lug grooves 25B, andthe lug grooves 25 provided in the shoulder land portions 23C arereferred to as shoulder land portion lug grooves 25C. The narrow grooves26 provided in the center land portion 23A are referred to as centerland portion narrow grooves 26A, the narrow grooves 26 provided in themiddle land portions 23B are referred to as middle land portion narrowgrooves 26B, and the narrow grooves 26 provided in the shoulder landportions 23C are referred to as shoulder land portion narrow grooves26C. The narrow grooves 26 that communicate with a terminating end ofone of the lug grooves 25 and connect to one of the main grooves 22 orthe auxiliary grooves 24 are referred to as communication narrow grooves26E. Additionally, in the pneumatic tire 1 according to the presentembodiment, a lug narrow groove 27 is provided where both the lug groove25 and the narrow groove 26 are present and connected.

As illustrated in FIG. 4, the lug groove 25 includes groove walls 25 bformed with a chamfer 25 c from the opening portion in the tread surface21 to a groove bottom 25 a. The lug groove 25 has a groove width W2ranging from 2 mm to 4 mm and a groove depth D2 less than that of themain grooves 22 and the auxiliary groove 24 ranging from 2 mm to 6 mm.As illustrated in FIG. 5, the narrow groove 26 includes groove walls 26b formed from the opening portion in the tread surface 21 to a groovebottom 26 a in the tire radial direction. The narrow groove 26 has agroove width W3 ranging from 0.4 mm to 1.0 mm and a groove depth D3 lessthan that of the main grooves 22 and the auxiliary groove 24 rangingfrom 3 mm to 6 mm. As illustrated in FIG. 6, the lug narrow groove 27includes the lug groove 25 and the narrow groove 26 formed in the groovebottom 25 a of the lug groove 25 in the extension direction of the luggroove 25. The sum of the groove depth D2 of the lug groove 25 and thegroove depth D3 of the narrow groove 26 makes an overall groove depth of6 mm or less, less than that of the main grooves 22 and the auxiliarygroove 24. Additionally, the groove depth D3 of the narrow groove 26 ofthe lug narrow groove 27 is preferably 70% or greater of the overallgroove depth (D2+D3) of the lug narrow groove 27 including the luggroove 25.

The center land portion lug grooves 25A provided in the center landportion 23A are disposed in the tire circumferential direction. Thecenter land portion lug grooves 25A communicate at both ends with thecenter main grooves 22A that form the center land portion 23A and dividethe center land portion 23A into a plurality of blocks disposed in a rowin the tire circumferential direction. Note that in the presentembodiment, the center land portion lug grooves 25A are composed overallof the lug narrow grooves 27 where both the lug grooves 25 and thenarrow grooves 26 are present.

The middle land portion lug grooves 25B provided in the middle landportion 23B on the vehicle outer side are disposed in the tirecircumferential direction. The middle land portion lug grooves 25Bcommunicate at both ends with the center main groove 22A and theshoulder main groove 22B that form the middle land portion 23B on thevehicle outer side and divide the middle land portion 23B on the vehicleouter side into a plurality of blocks disposed in a row in the tirecircumferential direction. Additionally, the middle land portion luggrooves 25B provided in the middle land portion 23B on the vehicle outerside communicate at one end with the shoulder main groove 22B that formsthe middle land portion 23B on the vehicle outer side and terminatesthere. Note that in the present embodiment, the middle land portion luggrooves 25B provided in the middle land portion 23B on the vehicle outerside are composed overall of the lug narrow grooves 27 where both thelug grooves 25 and the narrow grooves 26 are present.

The middle land portion lug grooves 25B provided in the middle landportion 23B on the vehicle inner side communicate at a first end withthe center main groove 22A that forms the middle land portions 23B onthe vehicle inner side and terminates at a second end within the middleland portion 23B on the vehicle inner side without reaching theauxiliary groove 24. Accordingly, the middle land portion 23B on thevehicle inner side is formed as a rib-like land portion. Note that inthe present embodiment, the middle land portion lug grooves 25B providedin the middle land portion 23B on the vehicle inner side are, at theterminating end portion, lug narrow grooves 27 where both the luggrooves 25 and the narrow grooves 26 are present. The communicationnarrow groove 26E extends from the narrow groove 26 of the lug narrowgroove 27 and communicates with the auxiliary groove 24.

The middle land portion lug grooves 25B provided in the middle landportion 23B on the vehicle outer side and the center land portion luggrooves 25A provided in the center land portion 23A are provided suchthat in a plan view they are one groove that passes through the centermain groove 22A on the vehicle outer side, with both ends at the centermain groove 22A between the middle land portion 23B on the vehicle outerside and the center land portion 23A facing one another. The center landportion lug grooves 25A provided in the center land portion 23A and themiddle land portion lug grooves 25B provided in the middle land portion23B on the vehicle inner side are provided such that in a plan view theyare one groove that passes through the center main groove 22A on thevehicle inner side, with both ends at the center main groove 22A betweenthe center land portion 23A and the middle land portion 23B on thevehicle inner side facing one another. Thus, the middle land portion luggroove 25B provided in the middle land portion 23B on the vehicle outerside, the center land portion lug groove 25A provided in the center landportion 23A, and the middle land portion lug groove 25B provided in themiddle land portion 23B on the vehicle inner side constitute one throughlug grooves 25 that passes through the center main grooves 22A. In otherwords, a plurality of the through lug grooves 25E are provided in thetire circumferential direction. The through lug grooves 25E intersectthe tire circumferential direction and pass through the center landportion 23A and the middle land portion 23B on the vehicle outer side.Also, the through lug grooves 25E open to the shoulder main groove 22Bon the vehicle outer side at a first end at the middle land portion 23Bon the vehicle outer side and pass through the center main groove 22A onthe vehicle inner side of the center land portion 23A and terminatewithin the middle land portion 23B on the vehicle inner side at a secondend without reaching the auxiliary groove 24.

The shoulder land portion lug grooves 25C provided in each of theshoulder land portions 23C are disposed in a row in the tirecircumferential direction and intersect the tire circumferentialdirection. The shoulder land portion lug grooves 25C open at a first endto a design end E, which is the outer end of the tread surface 21 of thetread portion 2 in the tire lateral direction, and terminate at a secondend within the shoulder land portion 23C without reaching the shouldermain groove 22B located inward of the shoulder land portion 23C in thetire lateral direction. Accordingly, the shoulder land portions 23C areformed as rib-like land portions. Note that in the present embodiment,the shoulder land portion lug grooves 25C provided in the shoulder landportions 23C are, at the terminating end portion, lug narrow grooves 27where both the lug grooves 25 and the narrow grooves 26 are present. Thecommunication narrow groove 26E extends from the narrow groove 26 of thelug narrow groove 27 and communicates with the shoulder main grooves22B. Additionally, terminating end portions of the shoulder land portionlug grooves 25C, which are lug narrow grooves 27, are disposed on theground contact edges T.

Herein, design end E refers to the outermost end of the tread portion 2in the tire lateral direction disposed outward of the ground contactedge T in the tire lateral direction, and is the outermost end of thetread portion 2 in the tire lateral direction where grooves are formed.In FIG. 2, the design end E is illustrated as being continuous in thetire circumferential direction. In other words, in the tread portion 2,when the tire is placed on a dry, flat road surface, the region from theground contact edge T to the design end E is a region which does nottypically come into contact with the ground.

Note that the shoulder land portion lug grooves 25C provided in theshoulder land portions 23C terminate within the shoulder land portions23C and are separated from the through lug grooves 25E described above.However, the first end of the through lug groove 25E, i.e. the end ofthe middle land portion lug groove 25B provided in the middle landportion 23B on the vehicle outer side that communicates with theshoulder main groove 22B, is disposed on an extension of the end portionwhere the shoulder land portion lug groove 25C provided in the shoulderland portion 23C on the vehicle outer side terminates within theshoulder land portion 23C. Additionally, the second end of the throughlug groove 25E, i.e. the end of the middle land portion lug groove 25Bprovided in the middle land portion 23B on the vehicle inner side, isdisposed on an extension of the end portion where the shoulder landportion lug groove 25C provided in the shoulder land portion 23C on thevehicle inner side terminates within the shoulder land portion 23C. Inother words, the lug grooves 25 that include the shoulder land portionlug grooves 25C provided in the shoulder land portions 23C and thethrough lug grooves 25E (the middle land portion lug grooves 25B of themiddle land portion 23B on the vehicle outer side, the center landportion lug grooves 25A of the center land portion 23A, and the middleland portion lug grooves 25B of the middle land portion 23B on thevehicle inner side) are disposed on a smooth, continuous curved line CUthat crosses the land portions 23A, 23B, 23C between the outer ends(design ends E) of the tread portion 2 in the tire lateral direction.Curved line CU refers to a line having only tangent lines with an angleranging from 40° to 90° with respect to the tire lateral direction.

The center land portion narrow grooves 26A of the narrow grooves 26provided in the center land portion 23A are disposed between adjacentcenter land portion lug grooves 25A in the tire circumferentialdirection and intersect the tire circumferential direction. The centerland portion narrow grooves 26A communicate with the center main groove22A on the vehicle inner side of the center land portion 23A at a firstend, and terminate within the center land portion 23A at a second endwithout reaching the center main groove 22A on the vehicle outer side ofthe center land portion 23A.

The middle land portion narrow grooves 26B provided in the middle landportion 23B on the vehicle outer side are disposed between adjacentmiddle land portion lug grooves 25B in the tire circumferentialdirection and intersect the tire circumferential direction. The middleland portion narrow grooves 26B communicate with the center main groove22A at the middle land portion 23B at a first end, and terminate withinthe middle land portions 23B at a second end without reaching theshoulder main groove 22B at the middle land portion 23B.

The middle land portion narrow grooves 26B provided in the middle landportion 23B on the vehicle inner side are disposed between extensions ofadjacent middle land portion lug grooves 25B in the tire circumferentialdirection and intersect the tire circumferential direction. The middleland portion narrow grooves 26B communicate at both ends with theshoulder main groove 22B at the middle land portion 23B and with theauxiliary groove 24. Thus, the middle land portion narrow grooves 26Bprovided in the middle land portion 23B on the vehicle inner side dividea portion of the middle land portion 23B between the shoulder maingroove 22B and the auxiliary groove 24 into a plurality of blocksdisposed in a row in the tire circumferential direction.

The shoulder land portion narrow grooves 26C provided in the shoulderland portions 23C are disposed between adjacent shoulder land portionlug grooves 25C in the tire circumferential direction and intersect thetire circumferential direction. The shoulder land portion narrow grooves26C communicate with the shoulder main grooves 22B at a first end andterminate at a second end within the shoulder land portions 23C near theouter ends of the tread portion 2 in the tire lateral direction (designends E) extending beyond the ground contact edges T.

Note that the shoulder land portions 23C are provided with recessedportions 28 near the outer ends of the tread portion 2 in the tirelateral direction (design ends E). The recessed portions 28 have acircular dimple shape and are formed between adjacent shoulder landportion lug grooves 25C in the tire circumferential direction in tworows in the tire lateral direction, a laterally inner row 28 a with tworecessed portions 28 in the tire circumferential direction and alaterally outer row 28 b with three recessed portions 28 in the tirecircumferential direction. Additionally, the recessed portions 28 of thelaterally outer row 28 b have a larger diameter than those of thelaterally inner row 28 a. The shoulder land portion narrow grooves 26Cprovided in the shoulder land portions 23C terminate at the recessedportions 28 at the second ends. In the present embodiment, the shoulderland portion narrow grooves 26C terminate at the recessed portion 28 ofthe laterally outer row 28 b centrally located in the tirecircumferential direction.

The pneumatic tire 1 according to the present embodiment includesprojections 31 in the center main grooves 22A. As illustrated in theenlarged cross-sectional view of a main groove of FIG. 7, the projection31 is provided projecting from the groove bottom 22 a of the center maingroove 22A. The projection 31 has a hemispherical shape with a smoothcurved surface that projects from the groove bottom 22 a of the centermain groove 22A. A plurality of the projections 31 are provided in thetire circumferential direction in accord with the periodic oscillationsof the center main groove 22A. A plurality of rows (two in the presentembodiment) of projections 31 provided in the tire circumferentialdirection in accord with the periodic oscillations are provided in thetire lateral direction. The projections 31 are formed with a lowerprojection height from the groove bottom 22 a than a wear indicator (notillustrated) disposed on the groove bottom 22 a of the center maingroove 22A. The wear indicator is a projection within the main groove 22that allows the degree of wear to be visually determined. The wearindicator of a tire for a passenger vehicle has a specified height fromthe groove bottom 22 a of 1.6 mm. Thus, the projections 31 project fromthe groove bottom 22 a with a height of less than 1.6 mm. Such aprojection 31 preferably has a hemispherical shape with a diameterranging from 0.4 mm to 1.5 mm and a projection height ranging from 0.2mm to less than 1.6 mm. Note that the projection 31 may also be providedon the groove bottom 22 a of the shoulder main grooves 22B.Additionally, the projection 31 may also be provided on the groovebottom 22 a of only one of the shoulder main grooves 22B.

FIG. 8 is a plan view of a tread portion of a pneumatic tire accordingto another example of the present embodiment.

A pneumatic tire 101 according to another example illustrated in FIG. 8is different from the pneumatic tire 1 described above in that bulgegrooves 22E are disposed in the shoulder main groove 22B on the vehicleinner side; in that a plurality of the center land portion narrowgrooves 26A of the center land portion 23A, a plurality of the middleland portion narrow grooves 26B of the middle land portion 23B on thevehicle outer side, and a plurality of the shoulder land portion narrowgrooves 26C of the shoulder land portion 23C on the vehicle outer sideare disposed in a row in the tire circumferential direction betweenpairs of the lug grooves 25 adjacent in the tire circumferentialdirection; in that the narrow grooves 26 of the lug narrow grooves 27 ofthe center land portion 23A and the middle land portion 23B on thevehicle outer side are zigzag narrow grooves 26F; in that hole portions32 are disposed in the center land portion narrow grooves 26A of thecenter land portion 23A, the middle land portion narrow grooves 26B ofthe middle land portion 23B on the vehicle outer side, and the shoulderland portion narrow grooves 26C of the shoulder land portions 23C; andin that no recessed portions 28 are disposed in the shoulder landportion 23C on the vehicle outer side. How the pneumatic tire 101 isdifferent will be described below, and portions identical to those ofthe pneumatic tire 1 described above are denoted with the same referencesigns and descriptions thereof are omitted.

A bulge groove 22E with a semi-circular bulge toward the middle landportion 23B on the vehicle inner side is disposed in the shoulder maingroove 22B on the vehicle inner side. The bulge groove 22E is disposedso as to bulge toward the middle land portion 23B at a positioncorresponding to the communication narrow groove 26E provided in theshoulder land portion 23C on the vehicle inner side.

A plurality of the center land portion narrow grooves 26A are disposedin a row in the tire circumferential direction between adjacent centerland portion lug grooves 25A in the tire circumferential direction. Inthe present embodiment, two center land portion narrow grooves 26A aredisposed in a row in the tire circumferential direction between adjacentcenter land portion lug grooves 25A in the tire circumferentialdirection. In an embodiment in which a plurality of the center landportion narrow grooves 26A are disposed in a row in the tirecircumferential direction between adjacent center land portion luggrooves 25A in the tire circumferential direction, the first ends andthe second ends of the center land portion narrow grooves 26A alternatesides in order in the tire circumferential direction. In other words, asillustrated in FIG. 8, uppermost center land portion narrow groove 26Acommunicates with the center main groove 22A on the vehicle outer side,the one under that communicates with the center main groove 22A on thevehicle inner side, and the one under that communicates with the centermain groove 22A on the vehicle outer side. Thus, the center land portionnarrow grooves 26 are disposed so as to communicate with the maingrooves 22 on alternating sides in the tire lateral direction in orderin the tire circumferential direction.

A plurality of the middle land portion narrow grooves 26B of the middleland portion 23B on the vehicle outer side are disposed in a row in thetire circumferential direction between adjacent middle land portion luggrooves 25B in the tire circumferential direction. In the presentembodiment, two middle land portion narrow grooves 26B of the middleland portion 23B on the vehicle outer side are disposed in a row in thetire circumferential direction between adjacent middle land portion luggrooves 25B in the tire circumferential direction. In an embodiment inwhich a plurality of the middle land portion narrow grooves 26B of themiddle land portion 23B on the vehicle outer side are disposed in a rowin the tire circumferential direction between adjacent middle landportion lug grooves 25B in the tire circumferential direction, the firstends and the second ends of the middle land portion narrow grooves 26Balternate sides in order in the tire circumferential direction. In otherwords, as illustrated in FIG. 8, uppermost middle land portion narrowgroove 26B of the middle land portion 23B communicates with the shouldermain groove 22B, the one under that communicates with the center maingroove 22A, and the one under that communicates with the shoulder maingroove 22B on the vehicle outer side. Thus, the middle land portionnarrow groove 26B are disposed so as to communicate with the maingrooves 22 on alternating sides in the tire lateral direction in orderin the tire circumferential direction.

A plurality of the shoulder land portion narrow grooves 26C provided inthe shoulder land portion 23C on the vehicle outer side are disposed ina row in the tire circumferential direction between adjacent shoulderland portion lug grooves 25C in the tire circumferential direction. Inthe present embodiment, two shoulder land portion narrow grooves 26Cprovided in the shoulder land portion 23C on the vehicle outer side aredisposed in a row in the tire circumferential direction between adjacentshoulder land portion lug grooves 25C in the tire circumferentialdirection.

The zigzag narrow grooves 26F are narrow grooves 26 formed in a zigzagshape provided in the groove bottom 25 a of the lug grooves 25 of thelug narrow groove 27 of the center land portion 23A and the middle landportion 23B on the vehicle outer side. The zigzag narrow grooves 26Fhave a zigzag shape within the groove width W2 of the center landportion lug grooves 25A of the center land portion 23A and the groovewidth W2 of the middle land portion lug grooves 25B of the middle landportion 23B on the vehicle outer side. The zigzag narrow grooves 26Fhave a groove width W3 and a groove depth D3 similar to that of thenarrow grooves 26 of the lug narrow grooves 27 described above. Thezigzag narrow grooves 26F oscillate at least three or more times withinone lug narrow groove 27. Additionally, one oscillation of the zigzagnarrow grooves 26F is formed by a short narrow groove and a long narrowgroove. This oscillation is repeated.

The hole portions 32 are disposed in the narrow grooves 26 includingcenter land portion narrow grooves 26A of the center land portion 23A,the middle land portion narrow grooves 26B of the middle land portion23B on the vehicle outer side, and the shoulder land portion narrowgrooves 26C of the shoulder land portions 23C. The hole portions 32expand the narrow grooves 26A, 26B, 26C in parts, and preferably, forexample, have a circular shape in a plan view with a diameter rangingfrom 0.5 mm to 1.0 mm and a depth ranging from 3 mm to 6 mm. The holeportions 32 are disposed in the extension direction of the narrowgrooves 26A, 26B, 26C. The center land portion narrow grooves 26A of thecenter land portion 23A and the middle land portion narrow grooves 26Bof the middle land portion 23B on the vehicle outer side terminate atone end within the respective land portions 23A, 23B, and a total ofthree hole portions 32 are disposed in each narrow groove 26A, 26B, withone at the terminating end and a plurality (two in the presentembodiment) disposed partway along the narrow grooves 26A, 26B. Notethat as no recessed portions 28 are provided in the shoulder landportion 23C on the vehicle outer side, the shoulder land portion narrowgrooves 26C of the shoulder land portion 23C on the vehicle outer sideterminate at the second end within the shoulder land portion 23C on thevehicle outer side, and the hole portions 32 are provided at theterminating ends. Additionally, a total of four hole portions 32 aredisposed in each shoulder land portion narrow groove 26C with aplurality (three in the present embodiment) disposed partway along. Inother words, the center land portion narrow grooves 26A of the centerland portion 23A, the middle land portion narrow grooves 26B of themiddle land portion 23B on the vehicle outer side, and the shoulder landportion narrow grooves 26C of the shoulder land portion 23C on thevehicle outer side terminate at the hole portions 32. Additionally, theshoulder land portion narrow grooves 26C of the shoulder land portion23C on the vehicle inner side terminate at the second end at therecessed portions 28, and a total of two hole portions 32 are disposedin each narrow groove 26A with a plurality (two in the presentembodiment) disposed partway along the narrow groove 26C.

The hole portions 32 provided in the center land portion 23A and thehole portions 32 provided in the middle land portion 23B on the vehicleouter side are disposed in rows in the tire circumferential directionand positioned offset in the tire lateral direction with respect tostraight lines SL (including the tire equator line CL) in the tirecircumferential direction. Specifically, the hole portions 32 providedin the center land portion 23A and the hole portions 32 provided in themiddle land portion 23B on the vehicle outer side are disposed in rowsin the tire circumferential direction and disposed partially on thestraight lines SL (including the tire equator line CL) in the tirecircumferential direction with positions offset in the tire lateraldirection. Additionally, the hole portions 32 provided in the shoulderland portions 23C are disposed in rows in the tire circumferentialdirection and positioned on the straight lines SL in the tirecircumferential direction without being offset in the tire lateraldirection. Note that the hole portions 32 are not disposed in the middleland portion narrow grooves 26B of the middle land portion 23B on thevehicle inner side.

In such a manner, the pneumatic tire 1, 101 of the present embodimentincludes the main grooves 22 extending in the tire circumferentialdirection in the tread surface 21 of the tread portion 2 and the landportions 23 adjacent to one another in the tire lateral direction formedby the main grooves 22. At least one of the main grooves 22 has awave-like shape with periodic oscillation. The groove bottom 22 a of thewave-like main groove 22 is provided with the projections 31 disposed ina row in the tire circumferential direction in accord with the periodicoscillations of the main groove 22.

According to the pneumatic tire 1, 101, the main grooves 22 have awave-like shape with periodic oscillation. This increases the overallwidth of the main grooves 22 to provide good drainage properties, andallows braking performance on wet road surfaces to be improved.Furthermore, according to the pneumatic tire 1, 101, the projections 31provided on the groove bottom 22 a of the wave-like main grooves 22makes the water at the groove bottom 22 a of the main groove 22turbulent to spread out and discharge the water out of the main groove22. This allows good drainage properties to be provided and brakingperformance on wet road surfaces to be improved.

Preferably, in the pneumatic tire 1, 101 of the present embodiment, theprojections 31 are disposed in a plurality of rows in the tire lateraldirection.

According to the pneumatic tire 1, 101, the projections 31 are disposedin rows in the tire lateral direction. This allows the water locatedoutward of the main groove 22 in the tire lateral direction to be spreadout and discharged. Thus, drainage properties can be further improvedand braking performance on wet road surfaces can be improved.

Preferably, in the pneumatic tire 1, 101 of the present embodiment, theprojections 31 are formed with a lower projection height from the groovebottom 22 a than a wear indicator disposed on the groove bottom 22 a ofthe main groove 22.

According to the pneumatic tire 1, 101, the projections 31 are formedwith a lower projection height from the groove bottom 22 a than a wearindicator, which is a projection within the main groove 22 that allowsthe degree of wear to be visually determined. This prevents the functionof the wear indicator from being inhibited by the projections 31.

Preferably, in the pneumatic tire 1, 101 of the present embodiment, fourmain grooves 22 are provided in the tread surface 21, each havingperiodic oscillation. The main grooves 22 form the center land portion23A, the middle land portions 23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder landportions 23C outwardly adjacent to the middle land portions 23B in thetire lateral direction. The projections 31 are disposed in the maingrooves 22 (center main groove 22A) between the center land portion 23Aand the middle land portions 23B.

According to the pneumatic tire 1, 101, the projections 31 are disposedto provide good drainage properties in the main grooves 22 between themiddle land portions 23B on either side of the center land portion 23A,which is the center land portion 23A in the center of the tread surface21 that contributes to the braking performance on wet road surfaces.This allows the obtained effect of improving braking performance on wetroad surfaces to be significantly.

The pneumatic tire 101 of the present embodiment includes the treadsurface 21 of the tread portion 2 including a plurality of main grooves22 extending in the tire circumferential direction and a plurality ofland portions 23 adjacent to one another formed by the main grooves 22.At least two adjacent main grooves 22 in the tire lateral direction havea wave-like shape with periodic oscillation. The lug grooves 25 (thecenter land portion lug grooves 25A and/or the middle land portion luggrooves 25B on the vehicle outer side) are disposed in the landportions(s) 23 formed between the wave-like main grooves 22 (the centerland portion 23A and/or the middle land portion 23B on the vehicle outerside) in a row in the tire circumferential direction, intersect the tirecircumferential direction, and communicate with the main grooves 22 atboth ends. The narrow grooves 26 (the center land portion narrow grooves26A and/or the middle land portion narrow grooves 26B on the vehicleouter side) are disposed between adjacent lug grooves 25 in the tirecircumferential direction in a row in the tire circumferentialdirection, intersect the tire circumferential direction, and have anarrower groove width than the lug grooves 25.

According to the pneumatic tire 101, two adjacent main grooves 22 in thetire lateral direction have a wave-like shape with periodic oscillation.This increases the overall width of the main grooves 22 and providesgood drainage properties, and allows braking performance on wet roadsurfaces to be maintained. Furthermore, according to the pneumatic tire101, the lug groove 25 are disposed in a row in the tire circumferentialdirection and communicate with the wave-like main grooves 22 at bothends. This allows good drainage properties to be provided, and brakingperformance on wet road surfaces to be maintained. Additionally,according to the pneumatic tire 101, by the narrow grooves 26 beingdisposed between adjacent lug grooves 25 in the tire circumferentialdirection, good drainage properties can be provided, the brakingperformance on wet road surfaces can be maintained, and by the narrowgrooves 26 communicating with the main groove 22 at the first end andterminating within the land portion 23 at the second end and having anarrower groove width than the lug grooves 25, a decrease in therigidity of the land portions 23 between the wave-like main grooves 22can be suppressed and wear resistance performance can be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, fourmain grooves 22 are provided in the tread surface 21, each havingperiodic oscillation. The main grooves 22 form the center land portion23A, the middle land portions 23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder landportions 23C outwardly adjacent to the middle land portions 23B in thetire lateral direction. The center land portion 23A and one of themiddle land portions 23B (on the vehicle outer side) are provided withthe lug grooves 25 and the narrow grooves 26.

According to the pneumatic tire 101, the center land portion 23A and oneof the adjacent middle land portions 23B on either side of the centerland portion 23A in the tire lateral direction have good drainageproperties. This allows braking performance on wet road surfaces to bemaintained. Also, by suppressing a decrease in rigidity of the centerland portion 23A and one of the adjacent middle land portions 23B oneither side of the center land portion 23A, the obtained effect ofimproving wear resistance performance can be significant.

Preferably, in the pneumatic tire 101 of the present embodiment, theother middle land portion 23B (on the vehicle inner side) is providedwith the auxiliary groove 24 having a narrower groove width than themain grooves 22 and extending in a linear manner in the tirecircumferential direction; and the middle land portion narrow grooves26B disposed in a row in the tire circumferential direction thatintersect the tire circumferential direction, the middle land portionnarrow grooves 26B each communicating with the main groove 22 locatedoutwardly adjacent in the tire lateral direction and the auxiliarygroove 24 at both ends and having a narrower groove width than the luggrooves 25.

According to the pneumatic tire 101, the middle land portion 23B greatlycontribute to drainage properties, and so by the middle land portion 23Bbeing provided with the auxiliary groove 24 extending in a linear mannerin the tire circumferential direction and the middle land portion narrowgrooves 26B, good drainage properties can be provided, and thus thebraking performance on wet road surfaces can be improved. Furthermore,the auxiliary groove 24 has a narrower groove width than the maingrooves 22, and the middle land portion narrow grooves 26B have anarrower groove width than the lug grooves 25. Thus, a decrease in therigidity of the middle land portion 23B can be suppressed, and wearresistance performance can be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, theother middle land portion 23B (on the vehicle inner side) is providedwith the middle land portion lug grooves 25B disposed in a row in thetire circumferential direction, the middle land portion lug grooves 25Bintersecting the tire circumferential direction, communicating with themain groove 22 located inward in the tire lateral direction at the firstend, and terminating within the other middle land portion 23B at thesecond end without reaching the auxiliary groove 24; and thecommunication narrow grooves 26E connecting the terminating ends of themiddle land portion lug grooves 25B and the auxiliary groove 24 andhaving a narrower groove width than the middle land portion lug grooves25B.

According to the pneumatic tire 101, in the other middle land portion23B, the other middle land portion 23B is provided with the middle landportion lug grooves 25B that communicate with the main groove 22 locatedinward in the tire lateral direction at the first end and terminatewithin the other middle land portion 23B at the second end withoutreaching the auxiliary groove 24 and the communication narrow grooves26E that connect the terminating ends of the middle land portion luggroove 25B and the auxiliary grooves 24. This provides good drainageproperties and allows braking performance on wet road surfaces to befurther maintained. Furthermore, the middle land portion lug grooves 25Bthat terminate within the middle land portion 23B are provided and thecommunication narrow grooves 26E have a narrower groove width than themiddle land portion lug grooves 25B. This allows a decrease in therigidity of the middle land portions 23B to be suppressed and wearresistance performance to be improved.

Preferably, in the pneumatic tire 101 according to the presentembodiment, the lug narrow grooves 27 in which the lug groove 25 and thenarrow groove 26 are present are disposed between the middle landportion lug grooves 25B and the communication narrow grooves 26E.

According to the pneumatic tire 101, the lug narrow grooves 27 aredisposed between the middle land portion lug grooves 25B and thecommunication narrow grooves 26E. This allows excessive changes inrigidity at the communicating portion between the middle land portionlug grooves 25B and the communication narrow grooves 26E to besuppressed, and wear resistance performance to be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, theshoulder land portions 23C are provided with the shoulder land portionlug grooves 25C disposed in a row in the tire circumferential directionthat intersect the tire circumferential direction, the shoulder landportion lug grooves 25C terminating without reaching the main groove 22located inward in the tire lateral direction of the shoulder landportion 23C (the shoulder main groove 22B); and the shoulder landportion narrow grooves 26C disposed between adjacent shoulder landportion lug grooves 25C in the tire circumferential direction thatintersect the tire circumferential direction, the shoulder land portionnarrow grooves 26C communicating with the main groove 22 located inwardof the shoulder land portion 23C in the tire lateral direction at an endportion and having a narrower groove width than the shoulder landportion lug grooves 25C.

According to the pneumatic tire 101, the shoulder land portion narrowgrooves 26C provide good drainage properties in the shoulder landportions 23C, and the terminating ends within the shoulder land portion23C allow a decrease in rigidity of the shoulder land portion 23C to besuppressed and wear resistance performance to be improved. Furthermore,according to the pneumatic tire 101, the shoulder land portion narrowgrooves 26C provide good drainage properties and allow brakingperformance on wet road surfaces to be improved. Additionally, theshoulder land portion narrow grooves 26C have a narrower groove widththan the shoulder land portion lug grooves 25C. This allows a decreasein rigidity of the shoulder land portions 23C to be suppressed and wearresistance performance to be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, theshoulder land portion narrow grooves 26C are provided in one of theshoulder land portions 23C (on the vehicle outer side) disposed betweenadjacent shoulder land portion lug grooves 25C in the tirecircumferential direction in a row in the tire circumferentialdirection.

According to the pneumatic tire 101, the shoulder land portion narrowgrooves 26C disposed in a row in the tire circumferential directionprovide good drainage properties and allow braking performance on wetroad surfaces to be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, thecommunication narrow grooves 26E are provided connecting the terminatingends of the shoulder land portion lug grooves 25C and the main groove 22located inward of the shoulder land portion 23C in the tire lateral (theshoulder main groove 22B), and have a narrower groove width than theshoulder land portion lug grooves 25C.

According to the pneumatic tire 101, the shoulder land portion narrowgrooves 26C that connect the terminating ends of the shoulder landportion lug grooves 25C and the main groove 22 provide good drainageproperties and allow braking performance on wet road surfaces to befurther maintained. Furthermore, the shoulder land portion lug grooves25C that terminate within the shoulder land portions 23C are providedand the communication narrow grooves 26E have a narrower groove widththan the shoulder land portion lug grooves 25C. This allows a decreasein the rigidity of the shoulder land portions 23C to be suppressed andwear resistance performance to be improved.

Preferably, in the pneumatic tire 101 according to the presentembodiment, the lug narrow grooves 27 in which the lug groove 25 and thenarrow groove 26 are present are disposed between the shoulder landportion lug grooves 25C and the communication narrow grooves 26E.

According to the pneumatic tire 101, the lug narrow grooves 27 aredisposed between the shoulder land portion lug grooves 25C and thecommunication narrow grooves 26E. This allows excessive changes inrigidity at the communicating portion between the shoulder land portionlug grooves 25C and the communication narrow grooves 26E to besuppressed, and wear resistance performance to be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, themain groove 22 (the shoulder main groove 22B) located inward of one ofthe shoulder land portions 23C (on the vehicle inner side) in the tirelateral direction is provided with the bulge grooves 22E that bulgetoward the other adjacent middle land portion 23B (on the vehicle innerside) at positions corresponding to the communication narrow grooves26E.

According to the pneumatic tire 101, the bulge grooves 22E are providedbulging toward the other adjacent middle land portion 23B (on thevehicle inner side) at positions corresponding to the communicationnarrow grooves 26E. This allows the bulge grooves 22E to function as acatchment for discharging water to the communication narrow grooves 26E,and allows braking performance on wet road surfaces to be furthermaintained.

Preferably, in the pneumatic tire 101 (1) of the present embodiment, theshoulder land portions 23C are provided with recessed portions 28 at theouter ends in the tire lateral direction, and the shoulder land portionnarrow grooves 26C terminate at the recessed portions 28 at the outerend portion in the tire lateral direction.

According to the pneumatic tire 101, the outer end portions of theshoulder land portion narrow grooves 26C in the tire lateral directionterminate at the recessed portions 28. This prevents loads acting on theouter end portions of the shoulder land portion narrow grooves 26C inthe tire lateral direction, and allows a decrease in rigidity of theshoulder land portions 23C to be suppressed and wear resistanceperformance to be improved.

The pneumatic tire 101 of the present embodiment includes the treadsurface 21 of the tread portion 2 including the main grooves 22extending in the tire circumferential direction and the land portions 23adjacent to one another formed by the main grooves 22. Adjacent maingrooves 22 in the tire lateral direction have a wave-like shape withperiodic oscillation. The lug grooves 25 are disposed in the landportions 23 formed between the wave-like main grooves 22 adjacent in thetire lateral direction in a row in the tire circumferential direction,intersect the tire circumferential direction, and communicate with themain grooves 22 at both ends. The zigzag narrow grooves 26F are disposedin the groove bottoms 25 a of the lug grooves 25 with a zigzag shape inthe extension direction of the lug grooves 25 and have a narrower groovewidth than the lug grooves 25.

According to the pneumatic tire 101, the main grooves 22 have awave-like shape with periodic oscillation. This increases the overallwidth of the main grooves 22 and provides good drainage properties, andallows braking performance on wet road surfaces to be maintained.Furthermore, according to the pneumatic tire 101, the lug grooves 25 andthe zigzag narrow grooves 26F provide good drainage properties, and howthe zigzag narrow grooves 26F mate suppresses a decrease in rigidity ofthe land portions 23 divided by the lug grooves 25. This allows wearresistance performance to be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, thezigzag narrow grooves 26F have the groove depth D3 which is 70% orgreater of the overall groove depth of the lug groove 25 including thegroove depth D2.

According to the pneumatic tire 101, the zigzag narrow grooves 26F havea groove depth that is 70% or greater of the overall groove depth. Thisallows the obtain effect of providing good drainage properties andimproving wear resistance performance to be significantly.

Preferably, in the pneumatic tire 101 of the present embodiment, thezigzag narrow grooves 26F oscillate at least three or more times.

According to the pneumatic tire 101, the zigzag narrow grooves 26Foscillate three or more times. This allows the obtained effect ofimproving wear resistance performance to be significant. Preferably, oneoscillation of the zigzag narrow grooves 26F is formed by a short narrowgroove and a long narrow groove, and this oscillation is repeated. Thisallows a decrease in rigidity of the land portions 23 divided by the luggrooves 25 to be further suppressed, and the obtained effect ofimproving wear resistance performance to be more significant.

Preferably, in the pneumatic tire 101 of the present embodiment, fourmain grooves 22 are provided in the tread surface 21, each havingperiodic oscillation. The main grooves 22 form the center land portion23A, the middle land portions 23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder landportions 23C outwardly adjacent to the middle land portions 23B in thetire lateral direction. The center land portion 23A and one of themiddle land portions 23B (on the vehicle outer side) are provided withthe lug grooves 25 and the zigzag narrow grooves 26F. The other middleland portion 23B (on the vehicle inner side) and the shoulder landportion 23C are provided with the lug grooves 25 without a zigzag narrowgroove 26F disposed in a row in the tire circumferential direction thatintersect the tire circumferential direction. The lug grooves 25 aredisposed on the smooth, continuous curved line CU that crosses the landportions 23A, 23B, 23C between the outer ends of the tread portion 2 inthe tire lateral direction.

According to the pneumatic tire 101, the lug grooves 25 are disposed onthe smooth, continuous curved line CU that crosses the land portions23A, 23B, 23C between the outer ends of the tread portion 2 in the tirelateral direction. This allows good drainage properties to be providedbetween the land portions 23A, 23B, 23C, and braking performance on wetroad surfaces to be maintained. Furthermore, the lug grooves 25 aredisposed on the smooth, continuous curved line CU that crosses the landportions 23A, 23B, 23C between the outer ends of the tread portion 2 inthe tire lateral direction. This allows an excessive difference inrigidity between the land portions 23A, 23B, 23C in the tire lateraldirection to be suppressed. Thus, wear resistance performance can beimproved.

Additionally, the pneumatic tire 101 of the present embodiment includesthe tread portion 2, a plurality of main grooves 22 extending in thetire circumferential direction in the tread surface 21 of the treadportion 2, and a plurality of land portions 23 adjacent to one anotherformed by the main grooves 22. The main grooves 22 have a wave-likeshape with periodic oscillation. The lug grooves 25 are disposed in theland portions 23 in a row in the tire circumferential direction andintersect the tire circumferential direction. The narrow grooves 26 aredisposed between pairs of the lug grooves 25 adjacent in the tirecircumferential direction in a row in tire circumferential direction,intersect the tire circumferential direction, and have a narrower groovewidth than the lug grooves 25. The hole portions 32 are formed in thenarrow grooves 26.

According to the pneumatic tire 101, the main grooves 22 have awave-like shape with periodic oscillation. This increases the overallwidth of the main grooves 22 and provides good drainage properties, andallows braking performance on wet road surfaces to be maintained.Additionally, according to the pneumatic tire 101, in addition toproviding good drainage properties with the lug grooves 25 and thenarrow grooves 26, a decrease in the rigidity of the land portions 23 issuppressed by the narrow grooves 26 having a groove width less than thatof the lug grooves 25. As a result, wear resistance performance can beimproved. Also, the effect of suppressing a decrease in the rigidity ofthe land portions 23 is maintained by the narrow grooves 26, and thehole portions 32 further improve drainage properties. As a result,braking performance on wet road surfaces can be maintained.

Preferably, in the pneumatic tire 101 of the present embodiment, fourmain grooves 22 are provided in the tread surface 21, each havingperiodic oscillation. The main grooves 22 form the center land portion23A, the middle land portions 23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder landportions 23C outwardly adjacent to the middle land portions 23B in thetire lateral direction. A plurality of narrow grooves 26 including thehole portions 32 are disposed in the center land portion 23A and one ofthe middle land portions 23B (on the vehicle outer side) in a row in thetire circumferential direction. The narrow grooves 26 having the holeportions 32 communicate with one of the main grooves 22 at the first endand terminate within the land portion 23 at the second end withoutreaching the other main groove 22, with the first ends and the secondends alternating sides in the tire lateral direction in the tirecircumferential direction.

According to the pneumatic tire 101, the center land portion 23A and oneof the middle land portions 23B (on the vehicle outer side) are landportions 23 that contribute to braking performance on wet road surfaces.The narrow grooves 26 having the hole portions 32 disposed in the landportions 23A, 23B in a row in the tire circumferential direction providegood drainage properties and improve braking performance on wet roadsurfaces. By the narrow grooves 26 having the hole portions 32terminating within the land portion 23 at the second end and having thefirst end and second end alternating sides in the tire lateral directionin the tire circumferential direction, the rigidity of the land portions23 can be made uniform. As a result, wear resistance performance can beimproved.

Preferably, in the pneumatic tire 101 according to the presentembodiment, the hole portions 32 provided in the center land portion 23Aand the hole portions 32 provided in one of the middle land portions 23B(on the vehicle outer side) are disposed in rows in the tirecircumferential direction and positioned offset in the tire lateraldirection with respect to straight lines SL in the tire circumferentialdirection.

According to the pneumatic tire 101, by the hole portions 32 havingpositions offset in the tire lateral direction with respect to thestraight lines SL in the tire circumferential direction, crackingbetween the hole portions 32 in the tire circumferential directionbetween the narrow grooves 26 disposed in a row in the tirecircumferential direction can be suppressed.

Preferably, in the pneumatic tire 101 according to the presentembodiment, the hole portions 32 provided in the center land portion 23Aand the hole portions 32 provided in one of the middle land portions 23B(on the vehicle outer side) are disposed in rows in the tirecircumferential direction and disposed partially on the straight linesSL in the tire circumferential direction with positions offset in thetire lateral direction.

According to the pneumatic tire 101, by the hole portions 32 havingpositions offset in the tire lateral direction with respect to thestraight lines SL in the tire circumferential direction, crackingbetween the hole portions 32 in the tire circumferential directionbetween the narrow grooves 26 disposed in a row in the tirecircumferential direction can be suppressed. By the hole portions 32being disposed partially on the straight lines SL in the tirecircumferential direction, this offset positioning in the tirecircumferential direction of the hole portions 32 suppressesnon-uniformity of the rigidity of the center land portion 23A and one ofthe middle land portions 23B (on the vehicle outer side). As a result,wear resistance performance can be improved.

Preferably in the pneumatic tire 101 of the present embodiment, theshoulder land portions 23C are provided with the narrow grooves 26including the hole portions 32.

According to the pneumatic tire 101, in addition to providing gooddrainage properties in the shoulder land portions 23C with the narrowgrooves 26, a decrease in the rigidity of the shoulder land portions 23Cis suppressed by the narrow grooves 26 having a groove width less thanthat of the lug grooves 25. As a result, wear resistance performance canbe improved. Also, an effect of suppressing a decrease in the rigidityof the land portions 23 is maintained by the narrow grooves 26, and thehole portions 32 further improve drainage properties. As a result,braking performance on wet road surfaces can be maintained.

Preferably, in the pneumatic tire 101 of the present embodiment, thehole portions 32 provided in the shoulder land portions 23C are disposedin rows in the tire circumferential direction and positioned on thestraight lines SL in the tire circumferential direction.

According to the pneumatic tire 101, non-uniformity of the rigidity ofthe shoulder land portions 23C in the tire circumferential directioncaused by the positions of the hole portions 32 can be suppressed, andthus wear resistance performance can be improved.

Preferably, in the pneumatic tire 101 of the present embodiment, theother middle land portion 23B (on the vehicle inner side) is providedwith the auxiliary groove 24 having a narrower groove width than themain grooves 22 and extending in a linear manner in the tirecircumferential direction, and the middle land portion narrow grooves26B without the hole portions 32 that communicate with the main groove22 located outwardly adjacent in the tire lateral direction and theauxiliary groove 24 at both ends and have a narrower groove width thanthe lug grooves 25.

According to the pneumatic tire 101, the middle land portion 23B greatlycontribute to drainage properties, and so by the middle land portion 23Bbeing provided with the auxiliary groove 24 extending in a linear mannerin the tire circumferential direction and the middle land portion narrowgrooves 26B, good drainage properties can be provided, and thus thebraking performance on wet road surfaces can be improved. Furthermore,the middle land portion 23B, though including the auxiliary groove 24,is not provided with the hole portions 32. Thus, a decrease in therigidity of the middle land portion 23B can be suppressed, and wearresistance performance can be improved.

EXAMPLES

In the examples, performance tests for braking performance on wet roadsurfaces were performed on a plurality of types of pneumatic tires ofdifferent conditions (see FIG. 9).

In these performance tests, pneumatic tires having a tire size of205/55R16 were assembled on 16×6.5J rims, inflated to the regularinternal pressure (200 kPa), and mounted on a test vehicle (1600 cc,front engine front wheel drive sedan passenger vehicle).

Braking performance on wet road surfaces was evaluated by measuring thebraking distance of the test vehicle from a speed of 100 km/h on a wetroad surface test course with a water depth of 1 mm. Then, themeasurement results were expressed as index values with the value of theConventional Example being defined as the reference (100). In thisevaluation, larger values indicate less braking distance, which ispreferable.

In FIG. 9, the pneumatic tires that were used as the test tires had aconfiguration including five land portions formed by four main grooves(two center main grooves and two shoulder main grooves) on the treadsurface, the land portions including the center land portion disposed onthe tire equatorial plane CL, the middle land portions disposed adjacentto the center land portion on the two sides in the tire lateraldirection, and the shoulder land portions disposed adjacent to themiddle land portions on the outer sides in the tire lateral direction.

The pneumatic tire of the Conventional Example indicated in FIG. 9include main grooves that oscillate in a wave-like manner. Additionally,the conventional pneumatic tire includes no projections on the groovebottom of the main grooves.

In the pneumatic tires of Examples 1 to 7, the main grooves oscillate inwave-like manner and include a projection on the groove bottom. In thepneumatic tires of Examples 1 to 5, the center main grooves include aprojection on the groove bottom. In the pneumatic tire of Example 6, theshoulder main grooves include a projection on the groove bottom. In thepneumatic tire of Example 7, all of the main grooves include aprojection on the groove bottom. In the pneumatic tire of Examples 1 and2, the projections are disposed in one row in the tire circumferentialdirection. In the pneumatic tire of Examples 3 to 7, the projections aredisposed in two rows in the tire circumferential direction. In thepneumatic tires of Examples 1 and 2, the projection height is 1.6 mm,the same as the wear indicator. In the pneumatic tires of Examples 3 to7, the projection height ranges from 0.2 mm to less than 1.6, less thanthe wear indicator.

As can be seen from the test results of FIG. 9, the pneumatic tires ofExamples 1 to 7 provided enhanced braking performance on wet roadsurfaces.

1. A pneumatic tire, comprising: a tread portion; a plurality of maingrooves extending in a tire circumferential direction in a tread surfaceof the tread portion, at least one of the plurality of main grooveshaving a wave-like shape with periodic oscillation; a plurality of landportions adjacent to one another in a tire lateral direction formed bythe plurality of main grooves; and a plurality of projections disposedon a groove bottom of the main groove having the wave-like shapedisposed in a row in the tire circumferential direction in accord withperiodic oscillations of the main groove having the wave-like shape. 2.The pneumatic tire according to claim 1, wherein the plurality ofprojections are disposed in a plurality of rows in the tire lateraldirection.
 3. The pneumatic tire according to claim 1, wherein theplurality of projections have a projection height from the groove bottomless than that of a wear indicator disposed on the groove bottom of thewave-shaped main groove.
 4. The pneumatic tire according to claim 1,wherein four of the plurality of main grooves are provided in the treadsurface, each having periodic oscillation; a center land portion, middleland portions adjacent to the center land portion on either side in thetire lateral direction, and shoulder land portions outwardly adjacent tothe middle land portions in the tire lateral direction are formed by themain grooves; and the main grooves between the center land portion andthe middle land portions comprise the projections.
 5. The pneumatic tireaccording to claim 2, wherein the plurality of projections have aprojection height from the groove bottom less than that of a wearindicator disposed on the groove bottom of the wave-shaped main groove.6. The pneumatic tire according to claim 5, wherein four of theplurality of main grooves are provided in the tread surface, each havingperiodic oscillation; a center land portion, middle land portionsadjacent to the center land portion on either side in the tire lateraldirection, and shoulder land portions outwardly adjacent to the middleland portions in the tire lateral direction are formed by the maingrooves; and the main grooves between the center land portion and themiddle land portions comprise the projections.
 7. The pneumatic tireaccording to claim 2, wherein four of the plurality of main grooves areprovided in the tread surface, each having periodic oscillation; acenter land portion, middle land portions adjacent to the center landportion on either side in the tire lateral direction, and shoulder landportions outwardly adjacent to the middle land portions in the tirelateral direction are formed by the main grooves; and the main groovesbetween the center land portion and the middle land portions comprisethe projections.
 8. The pneumatic tire according to claim 3, whereinfour of the plurality of main grooves are provided in the tread surface,each having periodic oscillation; a center land portion, middle landportions adjacent to the center land portion on either side in the tirelateral direction, and shoulder land portions outwardly adjacent to themiddle land portions in the tire lateral direction are formed by themain grooves; and the main grooves between the center land portion andthe middle land portions comprise the projections.